Disorganised atrial activity; AV node waiting for the next conducted impulse
average beats/min
The displayed value is the simulated average ventricular rate. Ten beats per minute is provided as a slow teaching speed. These settings are not clinical rate-control categories.
Controls. Use Play or Pause, Reset, the rate slider, or a preset. Ten beats per minute is a deliberately slow teaching speed. The other settings demonstrate simulated ventricular responses and should not be interpreted as clinical rate-control categories.
Colour key. Amber points illustrate unsynchronised atrial activation. They are a simplified teaching representation, not discrete anatomical foci. The blue SA node no longer determines the atrial rhythm. The green AV node permits only a variable proportion of atrial impulses to reach the ventricles. The amber ball represents a conducted impulse travelling through the His–Purkinje system. Red blush indicates depolarising myocardium. Teal indicates the simulated ECG trace.
Why the QRS is narrow. In this illustrated example, intraventricular conduction is intact. Conducted impulses activate the ventricles through the His–Purkinje system, producing narrow QRS complexes. A wide or changing QRS morphology during atrial fibrillation should prompt consideration of bundle branch block, rate-related aberrancy or ventricular ectopy.
Why it is irregularly irregular. Rapid, disorganised atrial impulses reach the AV node, but only a variable proportion are conducted to the ventricles. This produces R–R intervals with no repeating pattern, an important ECG recognition feature of atrial fibrillation.
Watch the baseline. No consistent discernible P waves are present. Fine fibrillatory baseline activity is illustrated here, although it may be subtle in clinical recordings. Select 10 beats/min to slow the teaching animation and follow one conducted impulse through the intact His–Purkinje system.
Teaching note. The six-beat R–R sequence repeats for teaching purposes. Clinical atrial fibrillation does not repeat in this way.
Educational illustration only.
This animation simplifies cardiac conduction. It is not a substitute for complete ECG interpretation, patient assessment or veterinary clinical judgement.